Your questions are not easy ones, for all depends how much time you have and the kind of money. Having both in abundance is useful and determines your route. You can go either west, or east. West via North America, Russia and China, or east via Turkey, Iran, and Pakistan. I assume that you will be going east. The problem spot here is the Anatolian highland in Turkey, for it will get very cold there after September. So, if taking that route, I suggest you leave in April, and be there when it's comfortable. You will be at a high altitude until you reach the Indus valley. Then it will get hot and humid. I was there last August and didn't find it unbearable, even on a motorcycle. You will get some rain, but usually a nice shower in the late afternoon. So be prepared and bring lots of money, preferably US$$$, then you can affort comfortable and safe hotels, and lots of
(except in Iran and Pakistan), and you will have fun, a lot of it.